it will all depend on the type of domains that you want and how you want to use them. then you can know where to buy and at how much.
I use multiple domain registrars because some tlds are cheaper at one place and other are on other places. The most commenly used registars by me are godaddy, namecheap, 101domain, ixwebhosting, inwx. Hope this will help.
yes if you new customer, .. I have remove to name cheap right now since their offer more cheapest than godaddy for registering new domain
If you factor in the cost of the domain plus privacy protection, Namecheap's prices are very good. Right now Namecheap has a $5.88 .com and that includes the first year of privacy protection free. After that, I think it is like $10.69 a year for a .com and privacy protection can be had for $0.99 a year with the special coupon code.